Liquid crystal display (LCD) device having an electrostatic discharge protection circuit and a high voltage supply circuit

Abstract

A Liquid Crystal Display (LCD) device having an Optically Compensated Bend (OCB) mode, which can restrict an initial high current while supplying a high voltage to a liquid crystal, includes: pixel circuits formed at crossing points of a plurality of scan lines and a plurality of data lines and including an Liquid Crystal (LC) capacitor of an OCB mode formed between a pixel electrode and a common electrode; an Electrostatic Discharge (ESD) protection circuit connected to each data line to prevent static electricity from accumulating in each pixel circuit; a DC-DC converter outputting a voltage for initial bend transition of the LC capacitor of the OCB mode; and a high voltage supplying circuit receiving a voltage of the DC-DC converter and transmitting a high voltage to the common electrode. An initial high current is prevented from flowing through the LC panel to thereby protect the LC panel and other elements from damage, and an initial bend transient time of the OCB mode liquid crystal is significantly reduced.

1. A Liquid Crystal Display (LCD) device, comprising:
 pixel circuits arranged at crossing points of a plurality of scan lines and a plurality of data lines and including a Liquid Crystal (LC) capacitor of an Optically Compensated Bend (OCB) mode arranged between a pixel electrode and a common electrode; 
 an Electrostatic Discharge (ESD) protection circuit connected to each data line and disposed to prevent static electricity from accumulating in each pixel circuit; 
 a DC-DC converter adapted to output a voltage for initial bend transition of the LC capacitor of the OCB mode; and 
 a high voltage supplying circuit connected between the DC-DC converter and the ESD protection circuit, 
 wherein resistance of the ESD protection current decreases only after a predetermined voltage is reached and the resistance depends on the magnitude of the voltage supplied. 
 
     
     
       2. The device of  claim 1 , wherein the high voltage supplying circuit comprises:
 a capacitor adapted to charge according to the voltage output by the DC-DC converter; and 
 a transistor adapted to output a current that varies according to a voltage charged in the capacitor. 
 
     
     
       3. The device of  claim 2 , wherein the high voltage supplying circuit further comprises a resistor connected between the DC-DC converter and the capacitor. 
     
     
       4. The device of  claim 3 , wherein the voltage charged in the capacitor is given by: 
       
         
           
             
               
                 vc 
                 ⁡ 
                 
                   ( 
                   t 
                   ) 
                 
               
               = 
               
                 
                   ( 
                   
                     1 
                     - 
                     
                       ⅇ 
                       
                         t 
                         RC 
                       
                     
                   
                   ) 
                 
                 ⁢ 
                 
                   V 
                   
                     d 
                     ⁢ 
                     
                         
                     
                     ⁢ 
                     c 
                   
                 
               
             
           
         
       
       where V c (t) is the voltage charged in the capacitor, V dc  is the voltage output by the DC-DC converter, and RC is a time constant. 
     
     
       5. The device of  claim 2 , wherein the transistor comprises a source connected to the DC-DC converter, a gate connected to the capacitor and a drain connected to the ESD protection circuit. 
     
     
       6. The device of  claim 5 , wherein the output current of the transistor is adapted to be cut off during a time that the capacitor is being charged. 
     
     
       7. The device of  claim 6 , wherein the voltage charged in the capacitor is adapted to be supplied to the ESD protection circuit after the capacitor has been completely charged. 
     
     
       8. The device of  claim 1 , wherein the high voltage supplying circuit is adapted to vary a current supplied to the pixel circuit according to a time that a bend transition voltage of the DC-DC converter is output. 
     
     
       9. The device of  claim 8 , wherein the high voltage supplying circuit is adapted to have a high resistance upon the bend transition voltage of the DC-DC converter being initially output, and wherein the high resistance of the high voltage supplying circuit is adapted to decrease to a low resistance over time. 
     
     
       10. The device of  claim 1 , wherein the ESD protection circuit comprises a transistor having a gate and a drain connected and adapted to be turned on upon a voltage of more than a predetermined level being supplied to the gate. 
     
     
       11. The device of  claim 10 , wherein the ESD protection circuit has a resistance adapted to decrease as the voltage supplied to the gate increases beyond the predetermined level. 
     
     
       12. The device of  claim 11 , wherein the predetermined level is 10 volts. 
     
     
       13. The device of  claim 1 , wherein the DC-DC converter is adapted to output a voltage of 15 to 30 volts. 
     
     
       14. The device of  claim 1 , wherein the data lines are adapted to be connected to ground upon the bend transition voltage being output by the DC-DC converter. 
     
     
       15. The device of  claim 1 , wherein the LC capacitor is connected in parallel to the ESD protection circuit. 
     
     
       16. The device of  claim 1 , wherein the pixel circuit further comprises:
 a switching transistor adapted to transmit a data voltage via the data lines to the pixel electrode in response to a selection voltage of the scan lines; and 
 a storage capacitor adapted to store the data voltage.